"G-d" is often used in writing so that G-O-D is not put down on paper and so cannot be burned or destroyed. A controversy exists over whether it is acceptable to spell out G-O-D on the internet--does it count as writing, or simply pixels? What if someone prints the window out? And so on.

In fact, there is a school of thought in which writing "god" in English or other non-Hebrew language is perfectly acceptable, in whatever form or medium. As the "Judaism FAQ" (http://www.faqs.org/faqs/judaism/FAQ/05-Worship/section-48.html) beautifully points out:

... the Shach (Yoreh De'a 179:11) ruled that "God" spelled in a foreign language does NOT have the status of a "shem" and thus may be erased, lehatkhila. There is a story about Rav Soloveitchik (z"l) intentionally writing GOD on the board while teaching a class and then just as deliberately and intentionally erasing it, so as to demonstrate by his own example that this was not a halakhically a problem.

"And ye shall overthrow their altars, and break their pillars, and burn their Asherot with fire; and ye shall hew down the graven images of their gods, and destroy the names of them out of that place. Ye shall not do so unto the Lord your God" (Deuteronomy 12:3-4).

The second of the above prohibitions is the one that results in Jews not writing down God's name, in order to prevent its accidentally being erased. In fact, if God's name has been written, such as in a Torah scroll or siddur, then Orthodox Jews customarily will never discard or burn the item on which the name is written. Instead, the now sanctified papers are buried in a cemetery or are stored permanently in a box called a geniza. Orthodoxy is currently divided as to whether typing God's name into a word processor or posting it on a web page is equivalent to writing it down. The closest thing there is to a consensus holds that it is not forbidden to erase God's name by changing pixels on a screen, such as in opening a new web page. However, it is forbidden to enable others to destroy or discard a printed manifestation of God's name. As such, one may not post God's name on a website, because this would allow the site viewers to print the name out and desecrate it.

The Tetragrammaton, spelled Yud-Hei-Vav-Hei, and its permutations Yud-Hei and Yud-Vav. The former is used as a suffix in words such as Hallelujah ("praise God"), and the latter is used as a prefix in names such as Yonatan ("God has given").

It's clear that the dual prohibitions above are intended to impart two things: 1) A reverence for God. 2) A sanctification of daily life and speech- people should invoke God, but should make sure their situations are perfectly and constantly holy first. Instead, the prohibitions have merely caused observant Jews to rename God, and then proceed to toss the new names around like trivialities.

Say I write you a letter, and in it write "Thank G-d, Moishie is doing well in cheder and little Rocheleh recovered from her flu". In this case, I have neither sincerely invoked God so as to thank him, or completely purged him from my prosaic recounting of everyday events. It's as if I've created an intermediary, worshiping God through the more accessible G-d.

Incidentally, this, according to the Maimonedes was the way that polytheism originated. He writes in the first chapter of Hilchot Avodat Kochavim that the generation of Enosh (Noah's grandson) reasoned that they were not holy enough to relate to God directly, so they began instead to worship his servants, the stars. Use of the spelling "G-d" implies an inferiority complex so pervasive it makes honest worship impossible.